In a conventional communication system in which a sensor transmits a detection signal to a control apparatus, the sensor and the control apparatus are configured to operate under the common time information. For example, as disclosed in US 2013/0343472 A1, the control apparatus generates a trigger signal as a request signal, and transmits the trigger signal to the sensor. In response to the request signal, the sensor transmits the sensor signal as a response signal to the control apparatus.
In US 2013/0343472 A1, it is considered that a trigger signal transmitted through a single signal line is branched on receiving end and two sensors simultaneously transmit respective sensor signals in response to the received trigger signals. In this configuration, even though two sensor values are acquired from respective two sensors, a data update cycle cannot be shortened compared with a case where the sensor value is acquired from a single sensor.
The data update cycle can be shortened by shifting acquisition time points of the sensor values from one another in a control apparatus. The shifting of the acquisition time points of the sensor values may be achieved by shifting transmission time points of the sensor signals including respective sensor values by a period shorter than the transmission cycle. Herein, the multiple sensor values are detected by respective sensing elements, and indicate detection result of a certain physical quantity. That is, the physical quantity to be detected by the multiple sensing elements is the same physical quantity of the same detection target.
In the above-described communication system, suppose that a microcomputer calculates a difference value indicating a difference of the multiple sensor values that are received, and the microcomputer further calculates a differential value by dividing the difference value by a time difference. In this case, when the output characteristic of each sensing element has an offset error or a variation in slope from one another, the difference value of the multiple sensor values cannot be calculated correctly.